Spectroscopic ellipsometry is a very power optical measurement technology widely used in semiconductor manufacturing, optical coating and material analysis. The ellipsometer measures the complex ratio of reflectivity of Rp and Rs, where Rp is the reflectivity of the electrical field whose direction is in the plane of incidence and Rs is the reflectivity of the electrical field whose direction is perpendicular to the plane of incidence. Both Rp and Rs are complex number and they are wavelength dependent.
The ellipsometric quantities are defined as:
            R      p              R      s        =                                                                  R              p                                      R              s                                                ·        exp            ⁢                          ⁢              ⅈ        ⁡                  (                                    δ              p                        -                          δ              s                                )                      =                            tan          ⁡                      (            Ψ            )                          ·        exp            ⁢                          ⁢      ⅈ      ⁢                          ⁢      Δ      
where
      tan    ⁡          (      Ψ      )        =                        R        p                    R        s                
andΔ=δp−δs 
δp and δs are the phases of Rp and Rs.
In conventional ellipsometer, in measuring the ellipsometric quantities, i.e. Ψ and Δ, it is necessary to rotate one of the polarizing components (the polarizer, analyzer or compensator) in the system. This limits the speed of the measurement. In some applications, it is desirable to perform measurements for a very small area (such as measuring the thin film thickness on semiconductor wafers). It is necessary to focus the light to a very small area.
Therefore, it is desirable to have spectroscopic ellipsometers capable of focusing on a small focus spot. It is further desirable to have an ellipsometer with minimal moving parts such that measurements can be taken without moving any mechanical parts in the system.